Bar code scanning system with offset optical axes

ABSTRACT

A scan module and an optical system such as for a bar code scanner wherein the optical system has an axis of outgoing (illumination) light offset from the axis of collected light, arranged to limit the dynamic range of the collected light and thus the dynamic range within which the bar code scanner detector and signal processor must function. Preferably, the outgoing axis and the collection lens axis are substantially parallel.

This application is a continuation of application Ser. No. 09/575,695filed Jul. 6, 2000, now U.S. Pat. No. 6,303,927, which is a divisionalof application Ser. No. 08/942,399 filed Oct. 1, 1997 U.S. Pat. No.6,166,375 which claims priority to provisional application Serial No.60/027,963 filed Oct. 8, 1996, each of which is incorporated byreference.

BACKGROUND

The field of the present invention relates generally to data capturesystems and more specifically to data readers, such as scanners and barcode reading devices.

Although the following description of this invention makes reference tobar code scanners, by way of example, the invention itself is equallyapplicable to other methods and systems for data reading and forms ofencoded data (indicia) other than bar codes.

From an operational point of view, bar code scanners are typicallyoperated in one of two modes, fixed or handheld. In the fixed mode ofoperation, objects with bar codes thereon are moved to or past astationary bar code scanner for scanning. In the handheld mode ofoperation, a portable bar code scanner is typically oriented and/ormoved to the bar code label to be read. For purposes of thisdescription, the term bar code scanner shall henceforth denote a scannerof the spot scanning type, wherein an illumination spot is moved acrossa bar code. The bar code scanners described herein may utilize anynumber of scan patterns comprising any number of scan lines in anyconfiguration suitable for bar code scanning applications and projectedthrough any number of scan windows. Further details regarding scanlines, scan patterns, and scan windows may be found in U.S. applicationSer. Nos. 60/010,935 and 08/792,829 entitled “Multi-Aperture Data Readerfor Multi-Mode Operation” and Ser. No. 60/021,783 and U.S. Pat. No.5,962,838 entitled “Bar Code Scanner with a Manually Switchable ScanPattern” herein incorporated by reference as if fully set forth herein.

A bar code label comprises a series of parallel dark bars of varyingwidths with intervening light spaces, also of varying widths. Theinformation encoded in the bar code is represented by the specificsequence of bar and space widths, the precise nature of thisrepresentation depending on the particular bar code symbology used.Methods for reading bar codes may comprise generation of an electronicsignal wherein a signal voltage alternates between two preset voltagelevels, one representing a dark bar and the other representing a lightspace. The temporal widths of these alternating pulses of high and lowvoltage levels correspond to the spatial widths of the bars and spaces.It is this temporal sequence of alternating voltage pulses of varyingwidths which is presented to an electronic decoding apparatus fordecoding.

A common and well-developed method for converting the spatial bar/spacesequence into a temporal high/low voltage sequence is the method of barcode reading. A bar code scanner typically has an optical system (alsoreferred to as an opto-mechanical system) with two subsystems: anillumination subsystem which produces an illumination beam and acollection subsystem which collects and detects light. The illuminationsubsystem, typically comprising a light source, a focusing lens, and ascan engine, focuses an outgoing light beam to a minimum diameter, knownas the waist, and generates a scan pattern so that the illuminationbeam, or spot, is likely to be scanned across a bar code. The collectionsubsystem, which typically includes a collection lens, or alternativelya concave collection mirror or functional equivalent thereof, and aphotodetector, collects at least some of the light scattered and/orreflected from the bar code illuminated by the illumination beam andfocuses the same onto the detector. The photodetector produces an analogsignal having an amplitude determined by the intensity of the collectedlight. The photodetector, for example, may generate a high voltage whena large amount of light scattered from the bar code impinges on thedetector, as from a light space, and likewise may produce a low voltagewhen a small amount of light scattered from the bar code impinges on thephotodetector, as from a dark bar. When the illumination and collectionpaths/axes are substantially coincidental, the system is typicallyreferred to as a retro-directive.

The illumination source in “spot” bar code scanners is typically alaser, but may comprise a coherent light source (such as a laser orlaser diode) or a non-coherent light source (such as a light emittingdiode). A laser illumination source offers the advantages of highintensity illumination which may allow bar codes to be read over a largerange of distances from the bar code scanner and under a wide range ofbackground illumination conditions (the area in which a bar code may beconsistently read by the scanning system is commonly referred to as thedepth of field). The scanner's ability to read bar codes at the outerextremes of the depth of field (far field) is, however, limited in partby collected optical power, which decreases approximately as the inverseof the square of the distance from the scanner. It is desirable for abar code scanner to be capable of reading bar codes over an extendeddistance from the scanner, that is, to have a large depth of field. Manyimprovements have been made to bar code scanners to extend their depthof field. One such improvement is disclosed in Rudeen et al. U.S. Pat.No. 5,479,011 entitled “Variable Focus Optical System For Data Reading”,the patent being hereby incorporated by reference. The Rudeen '011patent discloses a variable width aperture disposed in the outgoingoptical path thereby varying the location of the beam waist and enablingthe scanner to read bar codes over a greater depth of field. Anotherembodiment is disclosed in Bailey et al. U.S. Pat. No. 4,978,860entitled “Optical System for a Large Depth of Field Bar Code Scanner”,the patent being hereby incorporated by reference. The Bailey '860patent discloses a scanner utilizing a tilted detector array to extendthe depth of field of the reading device. Another improvement isdisclosed in Reddersen et al. U.S. Pat. No. 5,438,187 entitled “MultipleFocus Optical System for Data Reading Applications” the patent beinghereby incorporated by reference. The Reddersen '187 patent discloses asystem which utilizes a multiple focus lens as a means of extending thebar code scanner's depth of field.

There have been several other suggestions on how to increase the depthof field in previous bar code scanner systems. In another system, afocusing lens is designed with an axially movable lens element (such asa zoom lens) to permit changing the focusing power to change the depthof field. Such systems require complicated mechanical lens adjustmentand/or may require the user to manually make focusing adjustments. It isdesirable to eliminate the need for focus adjustments by the user orcomplicated mechanical devices.

Another previous method employed to improve depth of field for bar codescanning systems is over-filling the detector in the near field. Becausecollected optical power decreases approximately as the square of thedistance from the scanner, many bar code scanning systems amplify thedetected signal in order to read bar codes in the far field.Amplification boosts the detected signal generated by the photodetector.This amplification (or gain), however, boosts some detected signals,typically in the near field, to levels beyond the dynamic range of thebar code scanner's detection and signal processing systems. Althoughenabling a bar code scanner to read bar codes in the far field,amplification of detected signals generated from scanning bar codes inthe near field will frequently boost the detected signal to levelsoutside the functioning dynamic range of the detection and signalprocessing systems. Increasing the dynamic range of the detection andsignal processing systems (components) typically requires more expensiveand complex components with a potential concomitant deterioration of barcode scanner performance. That is, a lower first pass read rate of thebar code scanner and/or a higher mis-read rate. To improve the depth offield and first pass read rate of such systems, previous collectionsubsystems are designed to over-fill the detector in the near field.That is, the collection lens, or alternatively the collection mirror orfunctional equivalents thereof, is designed so the collected light inthe near field focuses a spot at the center of the detector which islarger than the detector, thereby over-filling the detector. All thecollected light is not detected, thereby limiting the dynamic range ofthe detected and processed signal. Many other secondary factors mayimpact the dynamic range, but it is nonetheless desirable to limit suchimpact. FIG. 7 is a plot of the power collected vs. the distance fromthe collection lens for a certain bar code scanning system andparticular conditions wherein the detector is filled when the bar codeis approximately 5.3 inches from the detector. As indicated in FIG. 7,the dynamic range is limited from approximately 800 nW to 2000 nW when abar code is scanned in a range of approximately 4-8.5 inches from thecollection lens. Consequently, bar codes over a greater depth of fieldmay be read for a given dynamic range of detection and signal processingsystems.

Other previous bar code scanning systems have had optical systems whichoffset the collection axis from the axis of outgoing light, however,significant differences and purposes exist in these previous systems.These optical systems were designed with an offset to minimize theamount of collected light the illumination focusing lens was keepingfrom reaching the detector while substantially coaxially aligning thecollection axis and the axis of outgoing light in retro-directive barcode scanning systems. Initially the two axes were very close together(approximately 0.1 inches apart) because the focusing lens wassuperimposed (off the central axis of the collection lens) in thecollection lens. Moreover, the collection lens and focusing lens werealigned such that their optical axes optimally converged within the scanvolume (were as close together as possible).

SUMMARY OF INVENTION

The present invention is directed to a method of data reading and anoptical system such as for a bar code scanner. In a preferredconfiguration, the optical system has an axis of outgoing (illumination)light offset from the axis of collected light, which limits the dynamicrange of the collected light and therefore the dynamic range withinwhich the bar code scanner detector and signal processor must function.Preferably, the outgoing axis and the collection axis are substantiallyparallel.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an illumination subsystem and acollection subsystem according to a preferred embodiment of the presentinvention.

FIGS. 2-6 depict the size and location of the collected and focused spoton the detector.

FIG. 7 is a graph of collected power versus distance for an opticalsystem which over-fills the detector in the near field.

FIG. 8 is a graph of collected power versus distance for an offsetoptical system.

FIG. 9 is a side perspective view of a scanner module with an outgoingoptical axis offset from the axis of the collection optics.

FIG. 10 is a cross sectional view of the scan module of FIG. 9 takenalong line 10—10.

FIG. 11 is a side perspective view of the scan module of FIG. 9 with theprinted circuit board removed to reveal internal components.

FIG. 12 is a front side perspective view of the scan module of FIG. 9with the printed circuit board removed to reveal internal components.

FIG. 13 is a top view of the scan module of FIG. 9 with the printedcircuit board removed to reveal internal components.

FIG. 14 is a bottom side assembly drawing of the printed circuit boardof the scan module of FIG. 9.

FIG. 15 is a top side assembly drawing of the printed circuit board ofthe scan module of FIG. 9.

FIG. 16 is a cross sectional view of an alternate scan moduleconfiguration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred and alternative embodiments of the subject invention will nowbe described in detail with reference to the drawings.

In a preferred configuration as shown in FIG. 1, the optical system isprovided with an axis 115 of outgoing (illumination) light offset fromand substantially parallel to the axis 135 of collected light to limitthe dynamic range. Offsetting the two axes will cause the spot generatedby the collection lens 130 to migrate across the detector 140 (or arrayof detectors) when bar codes 150 are read in the near field. Migrationlimits the dynamic range required of the detection and signal processingsystems because as the bar code moves closer to the collection lens,less of the light collected therefrom impinges on the detector 140 whenthe bar code 150 is scanned. Moreover, signal amplification may beincreased without exceeding the dynamic range of the detection andsignal processing systems, which enables the bar code scanner 10 to morereadily and reliably read bar codes in the far field. The depth of fieldis thereby extended such that the volume within which a bar code may besuccessfully scanned (i.e., scan volume) is larger, which, of course,increases the likelihood a bar code will be read during its first pass(when swept by or presented to the scanner).

Alternatively, signal amplification may be left unchanged therebyimproving the performance of the detection and signal processingsystems. The subject invention limits the dynamic range within which thedetection and signal processing systems must function. Detection andsignal processing components function optimally and bar code scanning isimproved (first pass read rate and reading accuracy) if these componentsare not pushed to their dynamic range limits. Alternatively, lessexpensive and/or complex components which are designed to work within asmaller dynamic range may be used without compromising bar code scannerperformance.

To offset the two axes, the focusing lens 110 may be located adjacent tothe collection lens 130 but not superimposed thereon (side by side).This arrangement keeps the focusing lens 110 from preventing light fromreaching the detector 140.

The outgoing axis 115 is preferably parallel to the collection axis 135,but may vary somewhat from absolutely parallel. In an actualconstruction the alignment of the axes 115, 135 varies by about 3°. Thusthe alignment may vary from substantially parallel (about +/−5°) or mayvary by even a greater amount (e.g. 10°) depending upon the particularconfiguration.

FIG. 1 illustrates an optical system 10 comprising light source 100(typically a visible laser diode), focusing optics 110 (preferably bothlight source 100 and necessary focusing optics are housed in a visiblelaser diode module), scanning mechanism downstream of focusing optics110 aligned on outgoing optical axis 115, detector 140 (preferably aphotodiode), and collection optics 130 aligned on collection opticalaxis 135, and an imaging photodetector 140 at focal plane 120. The scangenerating mechanism is not shown, but is well known and may compriseany suitable scanning mechanism such as a pivoting mirror, rotatingmirror, rotating hologram, or moving light source. An object 150 to bescanned with a bar code affixed thereto or printed thereon is shown atfocal plane 120. The offset of the two axes 115 and 135, as measured bydistance D3, causes the spot focused on detector 140 by collection lens130 to migrate across detector 140, and eventually off detector 140, asthe object 150 is moved progressively closer to collection lens 130 andis scanned. FIGS. 2-6 depict this migration. Other dimensions whichfigure prominently are D2, the distance from detector 140 to collectionlens 130, and D1, the distance from collection lens 130 to the bar codeto be scanned. In a preferred embodiment of the subject invention D1 isapproximately 15 inches, D2 is approximately 0.6 inches, D3 isapproximately 3 inches, and focal length of collection lens 130 isapproximately 0.6 inches, and the axis 115 is substantially parallel toaxis 135 (varying by about 3°). FIGS. 2-6 illustrate the location of thespot 105 at decreasing distance D as measured from the bar code scannernose (not shown) to the scanned bar code, wherein the distance from thecollection lens 130 to the nose is approximately 3 inches: </paragraph>

Figure D - Distance from scanner nose to barcode FIG. 2 270 mm FIG. 3170 mm FIG. 4  70 mm FIG. 5  20 mm FIG. 6  0 mm

As illustrated in FIGS. 2-6 not only does the center of the spot 105focused on detector 140 migrate farther from the center of the detectoras the bar code gets progressively closer to collection lens 130 (nearfield), but defocusing occurs, that is, the spot size grows larger. Asthe bar code scanned gets progressively closer to collection lens 130,the intensity of the light collected also increases as the inversesquare of the distance from collection lens 130. Therefore, asgraphically depicted in FIG. 8, the dynamic range is limited as a resultof a portion of the spot incident on detector 140 having migrated offthe detector 140.

Thus the optical system 10 provides an improved means of limiting thedynamic range. As shown by a comparison of the graphs of FIG. 7 and FIG.8, moving the collected spot off the detector (FIG. 8) lowers the powercollected more gradually than simply over-filling the detector (FIG. 7).Although a number of factors may impact these plots, migrating theincident spot off the detector has the advantage of limiting the dynamicrange over a greater depth of field. Offsetting outgoing optical axis115 from collected optical axis 135 limits the dynamic range to agreater degree than simply over-filling the detector.

Limiting the dynamic range has a number of benefits. Collected signalamplification may be increased without exceeding the dynamic range ofthe detection and signal processing systems when bar codes are scannedin the near field. Amplification enables the bar code scanner to readbar codes in the far field thereby extending the depth of field andincreasing the likelihood a bar code will be read during its first sweepby or presentation to the scanner. Other factors play a role in a barcode scanner's ability to extend its depth of field by signalamplification, including the bandwidth of the amplification system, spotsize in the far field, and the signal to noise ratio. Nonetheless, manysystems which offset the axis of outgoing light from the axis ofcollected light will be able to increase the amplification of thedetected signal which will enable the bar code scanner to read bar codesfarther from the scanner without compromising performance in the nearfield (i.e., extend the depth of field). An increase in the size of thedepth of field increases the scan volume within which a bar code may beread, which in turn increases the likelihood that a bar code presentedto or swept by the bar code scanner will be in the scan volume and thusbe successfully read. First pass read rate is a critical performancecriterion for bar code scanners.

On the other hand narrowing the dynamic range of a bar code scanningsystem while maintaining the depth of field may also be of benefit.Detection and signal processing systems are able to successfully readbar codes within a certain range of collected signals. In lieu ofincreasing amplification as a means of extending the depth of field whenthe subject invention is employed, alternatively amplification mayremain the same so that the detection and signal processing systemsexperience a more limited dynamic range, that is, a smaller dynamicrange. Detection and signal processing performance deteriorates at theextremes of their dynamic range. Limiting the dynamic range within whichthe detection and signal processing systems typically have to operateimproves detection and signal processing performance which in turnimproves bar code scanner performance (including edge detection, firstpass read rate, and scanning accuracy). Alternatively, less expensiveand/or complex components which are designed to work within a smallerdynamic range may be used without compromising bar code scannerperformance.

As depicted in FIG. 1, wherein collection lens 130 and focusing lens 110are side by side and not superimposed, focusing lens 110 does notprevent backscattered or reflected light from the scanned bar code fromreaching the detector 140. This arrangement allows the maximum lightpossible, for a given collection system, to be collected. Although thismay be undesirable when bar codes are scanned in the near field, it iscritical to bar code scanner performance in the far field and toextending the depth of field.

The various optical systems described above may be provided in efficientconfigurations incorporated into a scan module. FIGS. 9-13 illustrateone such scan module 400 incorporating the optical system of FIG. 1. Thescan module 400 includes (1) a main housing 450, (2) a ditheringassembly 401, (3) a laser diode module 452 and a collection lens 470mounted to the housing 450 via clamp 454, (4) a collection fold mirror472 positioned at 45° behind the collection mirror, and (5) a detector419 mounted to the underside of PCB 415 over collection fold mirror 472.

The collection lens 470 may be constructed from any suitable lensmaterial such as glass or plastic. The lens 470 is preferablyconstructed from plastic and integrally molded within its own plasticsupport bracket 471. The bracket 471 is readily assembled by sliding thebracket 471 into place within the housing 450. The bracket 471 includesa U-shaped end portion 471 a which securely attaches to a lip 451 in aside of the housing 450. This integral collection lens 470 and lensbracket 471 assembly reduces the number of module components therebysimplifying module structure and assembly.

The dithering assembly 401 comprises a dithering mirror 402 mounted tomirror bracket 403. A mounting member 414 mounted on a base or housingmember 450, bending member or flexure 412 is mounted between themounting member 414 and the mirror bracket 403. The mounting bracket 403is pivotally supported on the mounting member 414 via bending member412. Though they provide no function during normal operation, shockpin(s) 413 are included to constrain motion of the ditherer under highexternal mechanical conditions (such as when the unit is dropped) toprevent damage to the bending member 412. The drive magnet 404 is alsomounted on the mirror bracket 403 with the drive coil 406 mounted to thePCB 415. The feedback sensor 408 (such as a Hall effect sensor) ismounted to the underside of the PCB 415 (shown by the dashed lines inFIG. 9) in a position adjacent the feedback magnet 410 mounted to themirror bracket 403. The motion of mirror 402 is driven by passing anoscillating drive current through drive coil 406. The drive coil 406(shown by the dashed lines in FIG. 9) is attached to the underside ofPCB 415, the actuator coil leads 407 of the drive coil 406 extendingthrough the board 415. When the PCB 415 is installed, the drive coil 406is positioned in the recess 405 adjacent the actuator magnet 404. Travelstops 416, 416 are positioned to restrict the amplitude of the ditheringmotion to a maximum dithering amplitude.

In operation, the laser diode module 452 generates a laser beam 460which is focused by a collimating lens located within the module barrel,passed through the exit slot, and directed onto the dithering mirror402. The laser diode module 452 is positioned adjacent to the collectionlens 470. The collection lens 470 has a cutout notch 473 on one sidewithin which the diode module 452 is positioned thereby providingfurther compactness of structure and enabling the diode 452 to belocated closer to being coaxial with the collection lens 470. Thedithering mirror 402 oscillates to produce a scan line. Return signalreflected and/or scattered off an object (e.g. the bar code symbol on anitem being scanned) returns to the dithering mirror 402 and is directedto collection mirror 470 which focuses the return beam which isreflected by 45° fold mirror 472 up to the detector 419 (such as aphotodiode). The detector 419 detects and converts the signal intoelectrical impulses corresponding to, in the case of reading a barcodesymbol, the bars and spaces.

The system may comprise additional laser beam focusing features such asdescribed in U.S. Pat. Nos. 5,565,668 and 5,641,958 herein incorporatedby reference.

The dithering mirror 402 may be a flat mirror as shown or alternatelymay be curved thereby providing focusing power. The mirror 402 mayalternately include a small inset mirror attached to or molded with themirror 402 for reflecting the outgoing beam 460.

The scanner PCB 415 is also configured to provide for compactconstruction. FIG. 14 is a bottom side assembly drawing of the printedcircuit board 415 of the scan module 400 of FIG. 9. Several scannercomponents are efficiently mounted on the underside of PCB 415 includingthe detector 419, the actuator coil 406 and the Hall sensor 408. Theonly electronic component not mounted to the PCB 415 is the laser diodemodule 452. The leads 453 of the diode module 452 are connected to theconnectors 456 on the PCB 415 by a ribbon cable (not shown). The ribboncable exerts minimal forces on the diode module 452 minimizing potentialfor misalignment.

FIG. 15 is an assembly drawing of the top side of the PCB 415illustrating that the top side of the board contains additionalelectronic components. By mounting components on both sides of theboard, the size of the printed circuit board may be minimized with allmodule electronics mounted on a single board. Further description of thePCB 415 and the dithering assembly 401 is contained in James E. Colleyet al. “DITHERING ASSEMBLIES FOR BARCODE SCANNERS” filed Sep. 19, 1997U.S. application Ser. No. 08/934,487 U.S. Pat. No. 6,152,372 hereinincorporated by reference.

FIG. 16 is a cross section of an alternate scan module with a viewsimilar to the cross section of FIG. 10, wherein the diode module 452′is mounted to the PCB 415 enabling all the electronic components of thescan module 400 to be compactly and efficiently assembled on a singleprinted circuit board. By locating the diode module 452′ either on thePCB 415 or adjacent thereto, it may be possible to connect the leads(not shown) of the diode 452′ directly to the PCB 415 eliminating theneed for the ribbon cable of the previous configuration.

In the scan module 400 of FIGS. 9-13, the axis 460 of the outgoing beamand the axis 470 a of the collection lens 470 are offset by an amount D3(as defined in the schematic of FIG. 1). The D3 offset in module 400 isabout 0.25 inches. The offset amount for D3 is selected to provide thedesired degree of beam movement to correspond to desired limiting ofdynamic range. Referring to FIGS. 2-6 and 8, the smaller D3, the lessspot movement as the item is moved closer to the scanner. As shown inFIG. 8, as the amount D3 approaches zero, that is as the two axes 115,135 of FIG. 1 approach coaxial, the power on detector approaches thedashed line. The larger D3, the more spot movement and the more rapidlythe power on detector, designated by the solid line, drops off. If D3becomes too large, then the spot may fall entirely off the detector atnear field and the power on detector would fall to zero. Thus, byexperimentation for a particular scanner configuration, D3 may beempirically chosen to provide the desired limiting of dynamic range.

In an alternate embodiment, means may be provided to adjust the offsetD3 thereby providing adjustable limiting of dynamic range. Such meansfor adjusting the offset D3 may comprise, for example, suitablemechanical mechanisms which adjust the position of the beam axis 115,the source 100, the lens 110 or the lens 130. Such a suitable mechanismmay comprise a mechanical mechanism 455 which adjusts the position ofthe light source (diode module 452). Alternately, the offset D3 may beadjusted electro-optically such as via multiple beam sources,electrically controlled LCD element(s), or piezoelectric element(s).

A band pass filter, corresponding to the wavelength of the optical beam,may be provided in the collection path to prevent light of unwantedwavelength from reaching. The filter (not shown) may comprise a smallglass element attached directly to the detector 408 via double sidedtape or other suitable means and may be approximately the same size asthe detector.

Alternately, a corrective optical element, such a diffuser plate, may bedisposed between the collection lens 470 and the detector 408 such asdescribed in application Robert W. Rudeen et al. Ser. No. 60/054,962entitled COLLECTION SYSTEM FOR RANGE ENHANCEMENT filed Aug. 7, 1997hereby incorporated by reference. The corrective optical element mayprovide further range enhancement. The corrective optical element may beconveniently attached directly to the detector 408 or to the band passfilter described above thereby minimizing size and cost of manufacture.The corrective optical element and the band pass filter may comprise: asingle combined optical element; two separate optical elements mountedtogether or separately.

Certain aspects of the preferred embodiments described above may haveone or more of the following advantages:

to provide an optical system for a bar code scanner wherein a reduceddynamic range is required of signal detection and processing systems;

to provide an optical system for a bar code scanner which has a largerdepth of field;

to provide an optical system for a bar code scanner which improves barcode scanning performance;

to provide an optical system for a bar code scanner wherein thedetection and signal processing systems may be simplified withoutcompromising bar code scanner performance;

to provide a simplified optical system producing a compact scan modulewithout compromising bar code scanner performance;

to provide a scanning system or scan module with a simplified electroniccollection system without electronic gain control;

to provide a compact and efficiently constructed scan module;

to provide an optical system for a bar code scanner wherein the focusinglens does not prevent backscattered or reflected light from reaching thedetector.

Though certain examples and advantages have been disclosed, furtheradvantages and modifications may become obvious to one skilled in theart from the disclosures herein. The invention therefore is not to belimited except in the spirit of the claims that follow.

What is claimed is:
 1. A method of data reading comprising the steps ofgenerating an optical beam and directing the optical beam along anoutgoing axis toward an object to be read; scanning the optical beamwith a scanning mechanism for producing at least one scan line towardthe object; collecting incoming light scattered and/or reflected fromthe object via the scanning mechanism to a collection element andfocusing the incoming light into a spot on a detector; offsetting theoutgoing axis of the optical beam from an incoming axis of thecollection element; setting focusing arrangement for the collectionelement to form a small spot on the detector for an object located at afar range and to form a larger spot on the detector for an objectlocated at a near range, and causing a portion of the larger spot tofall off the detector at the near range.
 2. A method according to claim1 further comprising arranging the outgoing axis of the optical beamparallel to the collection axis of the collection element.
 3. A methodaccording to claim 1 wherein the outgoing axis and the collection axisare arranged substantially parallel +/−5° to each other.
 4. A method ofdata reading comprising generating an optical beam and directing italong an outgoing axis toward an object to be read; scanning the opticalbeam with a scanning mechanism for producing at least one scan linetoward the object; collecting incoming light scattered and/or reflectedfrom the object via the scanning mechanism to a collection element andfocusing the incoming light into a spot on a detector; offsetting theoutgoing axis of the optical beam from an incoming axis of thecollection element; causing the spot to migrate across and partially offthe detector when the object being read is located in a near field.
 5. Amethod of data reading comprising generating an optical beam anddirecting it along an outgoing axis toward an object to be read;scanning the optical beam with a scanning mechanism for producing atleast one scan line toward the object; collecting incoming lightscattered and/or reflected from the object via the scanning mechanism toa collection element and focusing the incoming light into a spot on adetector; offsetting the outgoing axis of the optical beam from anincoming axis of the collection element; causing the spot to migrate onthe detector such that as the object being read is moved nearer thecollection element, an increasing portion of the spot falls off thedetector.
 6. A method of data reading comprising generating an opticalbeam and directing it along an outgoing axis toward an object to beread; scanning the optical beam with a scanning mechanism for producingat least one scan line toward the object; collecting incoming lightscattered and/or reflected from the object via the scanning mechanismvia a collection element and focusing the incoming light into a spot ona detector; offsetting the outgoing axis of the optical beam from anincoming axis of the collection element; causing the spot to migrate onthe detector such that a decreasing portion of the spot falls on thedetector as the object is located nearer to the detector.
 7. An opticalscanning method comprising the steps of generating an optical beam anddirecting it along an outgoing axis toward an object to be read;scanning the optical beam with a scanning mechanism for producing atleast one scan line toward the object; collecting incoming lightscattered and/or reflected from the object via the scanning mechanism toa collection element and focusing the incoming light into a spot on adetector; offsetting the outgoing axis of the optical beam from anincoming axis of the collection element; increasing a portion of thespot which falls off the detector as the object is located nearer to thedetector.
 8. A scanner for scanning an optical code comprising: a laserfor projecting a laser beam in an outbound path at the optical code, andeffecting back scattered light therefrom in an opposite inbound path; adetector; a collection lens optically aligned with said laser in bothsaid outbound and inbound paths, and having an optical axis laterallyoffset from said laser, said collection lens focusing back scatteredlight to a spot toward said detector, wherein said detector is laterallyoffset from said laser, and optically aligned with said collection lensfor receiving said scattered light therefrom such that dynamic range ofthe incoming light reaching said detector is limited by causing the spotto be positioned completely on the detector when the optical code beingscanned is located in a far field and causing the spot to be positionedpartially off said detector when the optical code being scanned islocated in a near field.
 9. A scanner according to claim 8 wherein saidcollection lens includes a hole or notch extending therethrough andlaterally offset from said optical axis.
 10. A scanner according toclaim 9 wherein said laser is disposed in said hole or notch.
 11. Ascanner according to claim 9 wherein said hole or notch is spacedradially outward from said optical axis of said lens.
 12. A scanneraccording to claim 8 wherein said optical axis of said lens is parallelwith said laser.
 13. An optical scanning system comprising means forgenerating an optical beam and directing the optical beam along anoutgoing axis toward an object to be read; means for scanning theoptical beam with a scanning mechanism for producing at least one scanline toward the object; means for collecting incoming light scatteredand/or reflected from the object via the scanning mechanism to acollection element and focusing the incoming light into a spot on adetector; means for offsetting the outgoing axis of the optical beamfrom an incoming axis of the collection element; means for settingfocusing arrangement for the collection element to form a small spot onthe detector for an object located at a far range and to form a largerspot on the detector for an object located at a near range, and causinga portion of the larger spot to fall off the detector at the near range.14. A scanner for scanning an optical code comprising: means forgenerating an optical beam and directing it along an outgoing axistoward an object to be read; means for scanning the optical beam andproducing at least one scan line toward the object; mean for collectingincoming light scattered and/or reflected from the object via the meansfor scanning and focusing the incoming light into a spot on a detector,wherein the outgoing axis of the optical beam is offset from an incomingaxis of the collection element; means for causing the spot to migrateacross and partially off the detector when the object being read islocated in a near field.